1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device with RGBW pixels and a method of manufacturing the LCD device.
2. Description of the Related Art
LCD devices are considered to be the next generation of high technology and advanced display devices because of low power consumption and high portability.
Among the LCD devices, an active matrix type LCD device, which includes thin film transistors as switching units to drive its pixels independently, is mostly considered to the next generation of display device because of its high resolution and moving picture displaying ability.
A manufacturing process of the LCD device according to the related art includes forming an array substrate with thin film transistors and pixel electrodes, forming a color filter substrate with color filters and common electrodes, and forming liquid cells between the array substrate and the color filter substrate.
Such an LCD device is called a twisted nematic (TN) mode LCD device. The TN mode LCD device drives liquid crystal molecules disposed between the two substrates in a 90-degree twisted fashion by applying a voltage to the electrodes formed on the two substrates.
The TN mode LCD device according to the related art, however, has a considerable drawback of a narrow viewing angle. To solve the narrow viewing angle problem, LCD devices having various modes are being developed. For example, an in-plane switching (IPS) mode and an optically compensated birefringence (OCB) mode have been developed.
In the IPS mode LCD device, liquid crystal molecules are driven in parallel with substrates by an in-plane electric field generated by applying a voltage to two electrodes formed on the same substrate. That is, the long axes of the liquid crystal molecules are not erected with respect to the substrates. And, since the index of birefringence of the liquid crystal varies little in a clockwise direction, the IPS mode LCD device has a greatly improved viewing angle when compared with the TN mode LCD device according to the related art.
FIG. 1 is a cross-sectional view of an IPS mode LCD device according to the related art.
Referring to FIG. 1, the related art IPS mode LCD device includes a first substrate 118, a second substrate 119 attached to the first substrate 118, and a liquid crystal layer 130 injected between the first and second substrates 118 and 119.
By depositing metal on the first substrate 118 and patterning the deposited metal, a plurality of gate lines (not shown) are formed on the first substrate 118, and at the same time, a gate electrode 109 branched from the corresponding gate line is formed in each thin file transistor region.
A gate insulating layer 120 is formed entirely over the first substrate 118 including the gate electrode 109, and a semiconductor layer 115 including an active layer 115a and an ohmic contact layer 115b is formed on top of the gate insulating layer 120.
By depositing and patterning metal on top of the gate insulating layer 120, a plurality of data lines 110 (one data line is shown in FIG. 1) perpendicularly crossing the gate lines are formed on the gate insulating layer 120. Also, separated source/drain electrodes 116 and 117 are formed on the gate insulating layer 120 at a position appropriately related to the gate electrode 109. Further, a common line (not shown) and a plurality of common electrodes 113 are formed on the gate insulating layer 120.
Pixel regions are defined by the gate lines and the data lines 110 and a thin film transistor is provided in each pixel region. Further, each thin film transistor is formed by the gate electrode 109, the semiconductor layer 115, and the source/drain electrodes 116 and 117 in the corresponding pixel region. The common electrodes 113 are arranged in the pixel regions at predetermined intervals.
A protective layer 128 is formed entirely over the first substrate 118. A pixel electrode 114 is electrically connected with the drain electrode 117 in parallel with the common electrodes 113. A first alignment layer (not shown) is formed entirely over the first substrate 118.
A black matrix 121 is formed on the second substrate 119 to face the gate lines, the data lines, and the thin film transistors in order to selectively block light. A color filter layer 122 having red, green, blue color filter patterns is formed in open regions defined by the back matrix 121. An overcoat layer 123 planarizes a top surface of the color filter layer 122 and protects the color filter layer 122. A second alignment layer (not shown) is formed on the over coating layer 123.
Meanwhile, edges of the first and second substrates 118 and 119 are sealed up with a seal pattern (not shown) to prevent leakage of the crystal layer 130 interposed between the first and second substrates 118 and 119. A ball spacer 140 is interposed between the first and second substrates 118 and 119. The ball spacer 140, together with the seal pattern, maintains a predetermined gap between the first and second substrate 118 and 119.
The ball spacer 140 is made of glass fiber or organic material that has elasticity. Ball spacers 140 are randomly distributed through the first and second the substrates 118 and 119, which however causes the following problems.
Movement of the ball spacers 140 causes the alignment layers to detach. Further, attractive force of liquid crystal molecules around the ball spacers causes leakage of light around the ball spacers. Moreover, a cell gap cannot be stably kept using the ball spacers in a large-sized LCD device.
FIG. 2 is a cross-sectional view of a certain region of the second substrate 119 depicted in FIG. 1. Here, the certain region represents one RGB color filter pattern region defining one pixel. Referring to FIG. 2, the black matrix 121 is formed on the second substrate 119 in an evenly-spaced fashion. A red color filter pattern 122a, a green color filter pattern 122b, and a blue color filter pattern 122c are sequentially formed in the open regions defined by the back matrix 121. The red, green, and blue color filter patterns 122a, 122b, and 122c make up the color filter layer 122.
The overcoat 123 is formed on the color filter layer 122. The overcoat layer 123 is formed of organic material having a high polarization characteristic.
As mentioned above, in the second substrate 119 (color filter substrate), the red, green, and blue color filter patterns make up one pixel. However, in the case where the red, green, and blue color filter patterns make up one pixel, light transmittance is low and thereby brightness is also low.
Although the brightness of the IPS mode LCD device can be increased by increasing the brightness of the light generated by a backlight unit or the number of optical sheets in the LCD device, this increases manufacturing cost. Further, increasing current input to increase the brightness of the IPS mode LCD device destroys the desired low-power consumption characteristic of the LCD device.